Portable abrading and polishing machine



Aug. 21, 1956 J. D. HELBIG 2,759,305

PORTABLE ABRADING AND POLISHING MACHINE Filed June 11, 1954 5 Sheets-Sheet 1 INVENTOR.

T l 2 Jim D. Helbig BY gmw KATTORNEYE:

Aug. 21, 1956 J. D. HELBIG PORTABLE ABRADING AND POLISHING MACHINE 5 Sheets-Sheet 2 June Filed W ll INVENTOR.

- Jim 0. He/big 22 fil /Mg,

ATTORNEYS Aug. 21, 1956 J. D. HELBIG 2,759,305

PORTABLE ABRADING AND POLISHING MACHINE Filed June 11. 1954 s Sheets-Sheet s INVENTOR.

Jim D. He/big ATTORNEYS Aug. 21, 1956 J. D. HELBIG PORTABLE ABRADING AND POLISHING MACHINE 5 Sheets-Sheet 4 INVENTOR.

J'I'm D. Helbig Filed June 11, 1954 ATTORNEYS PORTABLE .ABRADING AND-POLISHING MACHINE IN V EN TOR.

Jim 0. Helbig BY ATTORNEYS United States Patent PORTABLE ABRADING AND POLISHING MACHINE Jim D. Helbig, Wheatridge, Colo., assiguor to Cyclo Manufacturing Company, Denver, Colo., a corporation of Colorado Application June '11, 1954, Serial No. 436,177

18 Claims. (Cl. 51-170) This invention relates to friction-type surface finishing machines and particularly to portable abrading and polishing machines. The present application is a continuation in part of application Serial No. 304,921 filed on August 18, 1952, now abandoned and of application Serial No. 339,695 filed on March 2, 1953, now abancloned.

Many types of portable abrading and polishing machines are known. Generally these machines comprise one or more motor driven friction heads arranged so that the operator may hold them in contact with the surface to be worked. The machines known heretofore include both single and multiple head types and many different types of mechanical drives and head supporting and guiding arrangements; such machines have been provided with single rotary heads, multiple heads with planetary drives, straight line reciprocating heads, and heads driven with non-linear translatory motion. The reaction forces produced upon engagement of the head with the working surface are transmitted from the machine to the hands of the operator; thus, in some machines violent vibration of the operators hands and consequent difliculty in handling the machine results, and in others, reactionary forces result in unbalanced abrading action, for example, it is well known that it is extremely diflicult to operate a single rotating sanding disk without undue gouging or uneven wear of the work. Various arrangements have been proposed to secure balanced operation of the machine and to minimize shaking or vibration tendencies of the machines, however, the machines embodying these arrangements have not proved entirely satisfactory for operations involving exacting requirements.

Some types of portable polishing machines have been designed heretofore with a view to duplicating the results of hand polishing because many operations require a high degree of finish which has been difficult or impossible to attain except through hand polishing operations. By way of an example of such operations, in the aircraft industry and in the servicing of aircraft, it is essential that the airfoil surfaces be given a high polish free from scratches, swirls or other marks. So exacting are the demands for perfection in the polishing of airfoil surfaces that it has been the universal practice heretofore to polish these surfaces by hand; this has resulted in very high maintenance costs and servicing delays. The various machines designed heretofore with a view to duplicating the results of hand polishing have met with limited success but have not found general acceptance for exacting operations such as that of the polishing of airfoil surfaces where an easily manipulated hand supported tool is essential. Accordingly, it is an object of this invention to provide a portable abrading and polishing machine including an improved arrangement for securing a finish equal or better than that obtainable through hand polishing.

It is another object of this invention to provide a porta- 2,759,305 Patented Aug. 21, 1956 ble polishing machine including an improved arrangement for securing stable operation and ease of handling.

it is another object of this invention to provide an improved portable polishing or abrading machine of the multiple head type.

It is another object of this invention to provide a portable abrading or polishing machine for elfecting polishmg with non-linear translatory motion and including an improved arrangement for minimizing reactive forces and facilitating the handling of the machine.

It is a further object of this invention to provide an improved abrading or polishing machine of the hand supported portable type and including an improved arrangement for minimizing the effect of reactive forces resulting from the engagement of the machine and the work surface.

It is a still further object of this invention to provide a portable abrading or polishing machine including an improved arrangement for minimizing the likelihood of the formation of scratches or marks which might result from the presence of foreign matter between the polishing head and the surface to be polished.

Further objects and advantages of this invention will become apparent as the following description proceeds and the features of novelty which characterize this inven tion will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly in carrying out the objects of this invention in one embodiment thereof, a portable abrading machine is constructed to comprise a main body having a pair of polishing heads mounted thereon for engagement with the work to be polished and a motor for driving the heads all mounted with suitable handles for carrying the machine by hand and for moving the machine about the surface to be polished. Each of the heads is rotatably mounted on a separate crank which is the sole support employed for positioning the head on the machine and thus provides a very simple assembly and mounting arrangement; the cranks are rotated by the common driving motor. The polishing heads are circular and have a radius substantially greater than the radius of the crank arms, and the heads are freely rotatable about their pivots at the ends of the crank arms. The crank arms are driven in the same direction and at the same speed but in opposed phase. A brief analysis will show that the centroidal axes of the heads are always moving in opposite directions and at equal velocities. The result of this driving connection is that the reactive forces occurring upon engagement of the two heads with the surface to be polished are equal and opposite and are balanced out, and only a slight intermittent torque occurring alternately in opposite directions is transmitted from the machine to the hands of the operator. The machine is provided with a handle which extends a substantial distance laterally of the center line of the heads so that the two heads resting on the work surface together with the operators hand supporting the handle provide a stable three point support for the machine. This greatly facilitates the manipulation of the machine during polishing and abrading operations. When the polishing heads are in contact with the work, the frictional forces between the work and the heads together with the inertia of the heads efifectively keep the heads from rotating about their axes at the ends of the crank arms and thus the movement of each head is essentially translatory; that is, all points on each head move in the same direction and at the same velocity at all times, each point moving through a circle having a radius equal to the length of the crank arm. Thus, although there is relative rotation of the heads with respect to the crank pins journalled therein, the heads themselves do not normally rotate appreciably when engaged with the work and may be said to be held substantially fixed with respect to their axes during the polishing operation except that a gradual drift is permitted as described below. The free rotary mounting of the heads on the crank arms also minimizes the likelihood of gouging or marking of the surface, should the head come into engagement with an obstruction or a foregin body on the surface because the head is then free to turn about its axis and thus it turns upon engaging an obstruction such as a large piece of grit or other foreign material and minimizes scratching or marking and also shock or pounding when the obstruction is large or stationary. Although the motion of the heads is essentially translatory they are free to rotate about their pivots or the crank pins and consequently they may drift slightly and change their positions with respect to one another and the machine. This drift has been observed in the operation of the heads and has been found to result in even wear of the surfaces of the head covers and also in increasing the self cleaning action of the covers. in another embodiment for certain applications, particularly when the heads are operated at low speed, the two heads may be tied together by a suitable member which affords relative movement of the heads on their respective crank arms but limits or prevents their rotation about their centroidal axes. In further embodiments three and four heads may be employed to secure certain of the advan tages of this invention.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

Fig. 1 is a perspective view of a portable polishing machine embodying the invention;

Fig. 2 is an elevation view partly in section of the polishing machine in Fig. 1;

Fig. 3 is a bottom plan view partly broken away illustrating the machine of Figs. 1 and 2;

Fig. 4 is an enlarged detail view of a modified form of drive mechanism;

Fig. 5 is a perspective view of another embodiment of the invention;

Fig. 6 is a sectional elevation view of the machine shown in Fig. 5;

Fig. 7 is a view similar to Fig. 6 showing amodified form of a drive;

Fig. 8 is a diagrammatic view showing the motion of theheads when driven by the device of Fig. 7;

Figs. 9 and 10 are diagrammatic illustrations of three and four head modifications of the invention;

Fig. 11 is a perspective view showing further embodiments of the invention;

Fig. 12 is a sectional plan view of the machine shown in Fig. 11;

Fig. -13 is a sectional view on the line 13-13 of Fig. 12;

Fig. 14 is a sectional view on the line 14-14 of Fig. 13; and

Fig. 15 is a sectional view along the line 15-15 of Fig. 13.

Referring now to the drawings, the embodiments of the invention shown in Figs. 1 through 4 inclusive are those disclosed in the aforesaid application Serial No. 304,921. The first of these embodiments as shown in Fig. 1 comprises a portable polishing or abrading machine having a main body or casing 20, a pair of polishing or abrading heads 21 and 22, and a detachable driving motor '23 secured on angle brackets 24 and 25 which are welded or otherwise suitably attached to the casing 20. The motor 23 is detachably secured to the angle braces 24 and 25 by straps or clamps 26. The operator may hold the machine and manipulate it by means of a handle 27 secured to'the forward end of the case and the bandle 28 of the'motor 23 which as illustrated is a type of motor commonly employed for operating hand drills, bufifers, sanders, and the like. As'shown in Figs. 2 and 3, the heads 21 and 22 are driven by agearing arrangement including a plurality of gears mounted within the case 20 and connected to be driven by the motor 23 through a pair of bevel gears mounted within a small rectangular housing 30 on top of the case 20. The motor is connected to drive a bevel gear 31 in the housing 30 through a universal or flexible joint 32 which permits some angular displacement of the motor shaft with respect to the shaft in the gear 31 The gear 31 drives a second bevel gear 33 at the upper end of a shaft 34 which carries a pinion gear 35 within the case 20. The heads 21 and 22 are mounted on crank arms 36 and 37 respectively, secured on shafts 38 and 39 parallel to the central shaft 34. The pinion gear 35 drives idler gears 41 and 42 which in turn drive gears 43 and 44 on the shafts 38 and 39 respectively. As shown in the drawing all the shafts of the gears are mounted in ball bearings to provide eflicient and quiet operation of the polishing machine. The arrangement of the gearing within the case 20 is such that the shafts 38 and 39 are driven in the same direction. The cranks 36 and 37 are secured to their shafts so that they are out of phase with one another. Thus as shown in Fig. 2, both cranks extend inwardly on the center line between the shafts so that the two polishing heads 21 and 22 are in their position nearest to one another. The radius of the cranks 36 and 37 is substantially less than the radius of the polishing heads 21 and 22, thus the entire area below each of the cranks is covered by the surface of the polishing head. The heads 21 and 22 are mounted on stub shafts 45 and 46 respectively rigidly secured to the outer ends of the crank arms. In Fig. 2 the polishing head 22 is shown in section and illustrates the mounting arrangement of the polishing heads whereby they are freely rotatable on the shafts 45 and 46. The polishing heads include hearing casings 47 and 48 respectively within which are mounted ball bearings in engagement with the stub shafts, these bearings being indicated at 49 in the sectional view of the polishing head 22. It will thus be apparent that as the crank arms 36 and 37 are rotated the polishing heads '21 and 22 are carried around with the stub shafts at the ends of the'arrns but are free to rotate with respect to the shafts. The inertia of the heads tends to prevent their rotation about their centroidal axes which coincide with the axes of the stub shafts, and when the machine -is:placed with the heads in contact with the work to be abraded or polished, the frictional forces between the work and the heads together with the inertia of the heads effectively prevent the rotation of the heads about their centroidal axes except for a slight drift. As a result of this free rotating mounting of the polishing heads 21 and 22 at the ends of the crank arms, the motion of the heads is essentially translatory while the heads are in contact with the surface tobe polished or abraded; thus,

-asthe crank arms 36 and 37 rotate, the heads follow themovement of-the crank arms but do not rotate about their own centroidal axes, rather the stub shafts 45 and 46 rotate within the bearings in casings 47 and 48. The translatory motion of the heads as shown in this embodiment'isessentially circular, that is, all points on each head-describe circles of the same diameter as the crank arm circle, each-point moving at the same velocity and in the same direction'as every other point on the head. This motion may be described as non-linear translatory motion. 'It'will readily be understood that this translatory motion is similar to that employed in hand polishing wherein the p'olishing cloth, brush, or other device is held in the handand moved'bodily in small circles. Because the heads can rotate about their crank pins they may drift somewhat sothat their motion is not identical to that obtained with hand polishing. This drift may occur as a slow and continuous rotation of the heads and has been found to facilitate the self cleaning action of polishing caps, such as those made of heavy napped cloth and further to result in more even wear of the cap material. The motion of the heads in this manner facilitates the obtaining of superior polished surfaces.

When the machine is to be employed on surfaces other than flat surfaces, it may be desirable that the heads be movable somewhat out of the common plane so that they may conform generally to the contour over which they are moved; for purposes of accomplishing this type of movement the arms 36 and 37 may be made of sufiiciently flexible material to permit their bending to facilitate the following of the contour of the surface being polished. The arrangement of the crank arms 36 and 37 so that they are 180 out of phase results in the cancelling or balancing out of the reactive forces produced between the polishing heads and the work surface when the heads are in engagement with the surface. These reactive forces which are transmitted to the body of the machine. and tend to Vibrate or displace the body during the operation of the machine are thus balanced out to minimize vibration. The crank arms 36 and 37 in Fig. 3 have been shown in positions rotated from that of Fig. 2 and extend at acute angles to the longitudinal line through the centers of the gear shafts. The 180 displacement of the two crank arms is indicated in the dot-and-dash lines corresponding to the center line of the crank 36 and a line normal to the center line and through the center of the shaft 39 of the crank 37, these lines being at right angles to one another as indicated. Both the cranks are rotated in the same direction as indicated by the arrows and thus the reactive force against the body of the machine caused by engagement of the head 22 with a surface to be polished tends to move the casing 20 upwardly as viewed in Fig. 3 while the reactive force caused by engagement of the head 21 and the surface tends to move the casing downwardly as viewed in this figure. Thus the two forces are equal and opposite and substantially cancel or balance out one another; however, it will be noted that because of the spacing of the shafts 38 and 39 a slight torque will occur which varies from zero to maximum during each half turn of the cranks and that this torque will be reversed when the cranks pass the vertical center lines through their shafts as viewed in Fig. 3. This torque is overcome for the most part by the inertia of the machine itself and the remaining torque is slight and easily controlled by the operator. intermittent, that is, it occurs alternately in opposite directions. The balancing of the reactive forces occurring on engagement with the surface to be polished or otherwise treated greatly facilitates the handling of the polishing Furthermore, the torque is machine and makes it possible for the operator to secure the full benefit of the non-linear translatory motion of the two heads. In the practical manufacturing application of this invention, in some cases it may be'difiicult to obtain the exact phase relationship of the cranks for balancing out of the reactive forces; and, furthermore, it has been found that some variation from the ideal phase relationship can be tolerated without producing undue shaking under load. For example, in one machine with two heads it was found that the phase differences could be in a range as wide as 170 to 190 without undue shaking of the machine although the operation was decidedly superior as the phase difference approached 180.

The multiple head machine disclosed herein provides advantages which cannot be realized with single head machines. The arrangement of two heads with the handle extending laterally of the plane of their drive shafts and equally spaced from the heads provides a stable working platform which forms the only natural stable support on an irregular surface and greatly increases the ease of handling; the stable platform is a result of the three point suspension of the machine, it being supported by the two heads and by the hand of the operator, the handle being located so that it minimizes any tendency to tilt the heads laterally and thus vary the distribution of load between heads. This is a symmetrical arrangement and the two heads are loaded equally. A further and important advantage resulting from the eifective balancing out of the reactive forces of the two heads is that the machine may be loaded heavily by pressing the heads against the work and will continue its polishing or abrading action up to the stalling point of the motor. In contrast the head of a single head machine having the same orbital drive tends to stop its abrading action whenever it is loaded, the head tending to stop in stationary contact with the work while the machine is moved with translatory motion about the centroidal axis of the head. This characteristic of operation makes the single head machine more difiicult to handle and greatly limits its effective working load. Another advantage of the machine with two heads is that the heads may be tipped about an axis parallel to the working surface and to the plane of the drive shafts so that they both rub relatively small areas without impairing their improved p-olishing action and freedom from shaking due to reactive forces; in this tipped position the heads continue to operate with non linear substantially translatory motion.

The freely rotatable heads as illustrated in the modification of Figs. 1, 2 and 3 are particularly advantageous in high speed machines, which may be operated to rotate the cranks at, say 3000 revolutions per minute. When one of the heads of a machine of this type is moved into engagement with an obstruction or object on the area to be treated the pounding or shock of the head against the object is minimized because on contact the head rotates and tend-s to roll away from the object without harsh impact. As a result, a machine of this type may be employed to polish areas which terminate, for example, in vertical walls. The machine may be moved over the area and against the wall and operate effectively to polish the area adjacent the wall without imparting undue shock or vibration to the machine and without the edges of the head tending to gouge or abrade the vertical surface.

For certain applications of this type of machine and particularly for large machines which are operated at lower speeds it may be desirable to provide an arrangement for positively assuring the non-linear translatory movement ofthe heads. In Fig. 4 there is illustrated an arrangement for accomplishing this purpose. In this figure a head 22a corresponding to the head of 22 of Figs. 1, 2 and 3 is provided with a shaft 50 which is journalled in a ball bearing assembly 51 mounted on a crank arm 37a corresponding to crank arm 37 of Fig. 2. A sprocket gear 52 is mounted at the upper end of the shaft 50 and an identical gear 53 is rigidly secured to the body 20 of the machine, it being shown secured to a housing 54 which encloses the bearing for the shaft of the crank 37a. The gears 52 and 53 are connected by a sprocket chain 55 and because the gears are the same size, rotation of the crank arm 37 causes the shaft 50 to remain stationary about its centroidal axis and to rotate within the bearing 51. The resulting motion of the head 22a is the same non-linear transl-atory motion described in connection with the embodiment of Figs. 1, 2 and 3; the sprocket chain 55 together with the gears 52 and 53 functioning to hold the head 22a positively so that it cannot rotate about its centroidal axis but must follow the movement of the crank 37a; thus all points of the head move in circles of the same diameter as that described in the crank. For some applications, particularly for heavy and low speed work, the advantage of maintaining non-linear translatory motion of the two heads by a drive as shown in Fig. 4 may be found to outweigh the advantage secured in the machine of Figs. 1, 2 and 3 where the head is free to rotate and may drift about its axis. The positive control or restraint prevents drifting rotation of the head about its centroidal axis and in some cases may prevent uneven operation due to drag caused, for example, by an accumulation of foreign matter which might cause the free head to rotate instead of following the translatory motion but which on the other hand might not be objectionable provided the head was restrained to movewith translatorymotion.

As illustrated in the drawings, the'heads 21 'and22 are covered with wool or sheepskin covers 57 and 58 respectively and these covers may of coursebe replaced with any type of polishing or abrading cover required for the particular work to be done. The head '22 as shown in Fig. 2 comprises a mounting plate 59 and soft body 59a which may be made of sponge rubber or other similar material to provide a cushioning effect. It has'been found that for sanding operations,'when asanding disc is secured to'the heads of the machine, it is possible to sand a floor or other area along a wall or around obstructions on the'floor without 'gougingor unevenwear of the surface.

In-Figs. and 6, thereis illustrated another embodiment of the invention in which a device is provided to prevent the rotation of the polishing heads about their own centroidal axes, thereby assuring substantially translatory motion of the heads under all conditions of operation. This modification is the same asthat disclosed in the above mentioned application Serial No. 339,695. In'the embodiment of'Figs. 5 and6, the main'body or casing of the machine is rectangular in form as indicated at 60 and the motor is mounted within a rearwardly extending casing 61 having a handle 62 at the far end thereof, a second handle 63 is provided on the casing 60. A pair of heads 64 and 65 are driven in the same direction and are freely rotatable with respect to their crank pins in the same manner as the heads 21 and 22 of Fig. 1, except that the restraining mechanism prevents their rotation about their own centroidal axes. The driving mechanism as shown in Fig. 6 comprises a worm 66 driven by the motor (not shown) within the casing 61. Three vertical shafts 67, 68 and 69 are mounted within ball bearing assemblies within the casing 60 in a manner similar to that of the shafts in the embodiment of Fig. 2. The shaft 67 is provided with a worm gear 70 which is driven by the worm 66 and sprocket gears 71 and 72 which are connected through sprocket chains 73 and 74 to drive sprockets 75 and 76 on the shafts 68 and 69 respectively. The heads 64 and 65 are freely rotatable on stub shafts or crank pins 77 and 78 which are secured rigidly in driving disks 79 and 80 respectively, attached to the outer ends of the shafts 68 and 69. Counterbalance weights 83 and 84 are provided within the casing 60 on the shafts 68 and 69 to minimize vibrations due to the centrifugal force of the rotating off-center mass of the shafts 77 and 78 and the heads attached thereto. The heads 64 and 65 are mounted on their respective shafts by ball bearing assemblies 85 and 86 respectively which are of the spherical type and allow limited rocking movement of the heads on the stubshafts; this provides the rocking movement which enables the heads to follow the contour of a round or uneven surface in the same manner as flexible crank arms in the modification of Fig. 1.

From the foregoing, it is readily apparent that the heads 64 and 65 are driven in the same direction by operation of the sprocket chain drive and, furthermore, the stub shafts 77 and 78 are mounted on the'shafts 68 and 69 so that they are 180 outof phase in the same manner as the stub shafts of the Fig. l embodiment. Any suitable finishing or abradingsurfaces may'be provided on the heads 64 and 65 and in Fig. 5, W001 butting covers 87 and 88 have been illustrated. It is readily apparent then that the operation of the machine shown member 91 and a rod 92 connected to the heads 64 arid'65, respectively,"and'in telescoping relationship. The tube 91 is "attachedto the head 64by a bracket 93 andthe-ro d"92is attached to the 'hea'd'65 by'a 'bracket 94. The lengths of-the'tube and the rod are such that during the operation of the machine even in-the extreme positions of theheads'6'4 and 65, the rod "92 is not drawn outof the tube 91. The end of'the-tube 91 opposite the'rod92 is open so-that no damping effect due to compression'of air by the reciprocation of the rod and the tube will result. "Theweights of the rod and tube assemblies are made 'equal-sothat unbalance due'to the restraining "attachment is minimized. It will now be evident that during operation'of the machine'the heads'64 and 65 will be held so that they remain in substantially'the same positions with respect to one another except *for their translatory motion produced by rotation of the cranks 77 and 78. The restraining'attachment thus acts to produce substantially the same eifect as'the sprocket chain arrangement illustrated in Fig. 4. The brackets 93 and'94 are pivotally attached to the heads on transverse pins 93a and 94a parallel to one another and to the top plates of their respective heads, the pins passing through the' brackets and through lugs 93b and 94b on the top plates; this pivotal mounting allows tilting of the heads whilethey are restrained to move in their translatory path.

'For'someapplications, it may be found desirable to rotate the c'ranks'in opposite directions and in opposite positions on their shafts when in alignment with the line through "the shafts. For example, if the cranks are mounted as shown in Fig.6, the stub shafts 77 and 78 extend in opposite directions and are then rotated in opposite directions. The reactive forces longitudinally [of the casing 60 will be cancelled, while the reactive forces at'right angles to the casing willbe the same in force and direction. 'A drive for obtaining opposite rotation of the two shafts is illustrated in Fig. 7, corresponding parts of the mechanism being designated by the same numerals as employed in 'Fig. 6 with the suffix a. The worm 66a drivestwo worm gears 70a and 70b, respectively, onshafts 67a and 67b, these shafts are thus rotated in opposite directions. In order that the shafts 68a and 69a may be spaced the required distance, a sprocket chain drive is provided which comprises chains 95 and'96 engaging gears 97 and 98 on the shafts 67a and'67b and gears 99 and 100 on the shafts 68a and 69a. The direction of rotation and relationship of the cranks and heads when drivenby the mechanism of Fig. 7 are shown in Fig.8.

Portable abrading or polishing machine embodying this invention and which are to be'employed as hand tools in the manner illustrated in Figs. 1 and 5, have been found to reproduce hand polishing in a highly effective manner. By providing two heads symmetrically'mounted on either side of the centerline, the loading on the two heads is easily made equal when the operator is holding the handles which are centrally located and thus the reactive forces produced by operation of the two heads are equal and are balanced out in the manner described above.

For some polishing, cleaning or abrading operations, it may be "found desirable to provide more than two polishing heads. In order to secure the advantages of this invention in machines requiring more than two heads, the heads may'be mounted and driven as indicated, by way of example, in Figs. 9 and 10 which illustrate schematically three and 'four head assemblies. In 'Fig. 9, three heads 102, 103 and 104 are connected on crank arms 105, 106 and 107 respectively, which are mounted apart and are rotated at the same speed and in the same direction by a suitable mechanism (not shown). In'this illustrati'on'the X and Y axes have been indicated and 'when'the "heads are driven 120 out of phase, both the X and Y'components of the reactive forces between the machine and the work surface cancel out, it being assumed that the machine is so mounted and held that equal loads are supported by the three heads.

In Fig. 10, four heads 108 109, 110 and 111 have been shown mounted on shafts 112, 113, 114 and 115 respectively, all the cranks extend inwardly toward the center and adjacent cranks are 90 apart. In this arrangement the cranks 112 and 113 rotate in the same direction and at the same speed and are 180 out of phase so that this pair of heads operates as do the pairs of heads in the modifications of Figs. 1 and The heads 110 and 111 are driven by the cranks 114 and 115 in the opposite direction from that of the cranks 112 and 113. The cranks 114 and 115 are arranged 180 out of phase and are rotated at the same speeds; thus the pair of heads 110 and 111 also operate in the same manner as the pairs of heads of Figs. 1 and 5. When the four heads mounted as indicated in Fig. are arranged to engage the surface to be polished, so that each head carries the same load, that is one-fourth of the total load, then both the X and Y components of the reactive forces between the machine and the work surface will cancel out. In addition, since the two sets of pairs of heads are rotated in opposite directions, the torques which exist in each pair of heads are also cancelled out. Undesirable shaking or vibration is thus minimized.

In Figs. 11 to there is illustrated a relatively small and compact tool of the same type as that illustrated in Fig. 1 but which is particularly suited to high speed applications and applications where smaller areas and greater curvature exist in the surfaces to be abraded, cleaned or polished. This machine is, of course, also suitable for the polishing of wide surfaces such as airfoil surfaces but because of its smaller size is admirably suited to operations where close quarters or small areas are involved. As shown in Fig. 11, the polishing machine comprises a main body 118 of generally triangular configuration having a motor 119 mounted on the upper side thereof and a handle 120 extending rearwardly from the body 118. A second handle 121 is provided directly over the front end of the machine. A pair of polishing heads 122 and 123 are mounted directly below the fore end of the machine and generally at the base corners of the triangle formed by the body 118. The electric power for operating the motor 119 is supplied through a suitable cable 124 and the operation of the motor is controlled by a toggle switch 125.

The operating mechanism and its details of construction are shown in Figs. 12 through 15 inclusive. Referring now to these figures the body 118 of the machine comprises a main casing 126 which is of generally triangular form and is extended at the rear apex of the triangle to form the handle 120 within which the mechanism (not shown) of the switch 125 is mounted. The switch 125 is connected to the motor 119 by leads 127. The main case 126 is closed by a cover plate 128 on which is mounted the casing of the motor 119. At the center of the lower wall of the casing 126 there is provided a heavy bearing boss 130; and lying at the two forward corners of the triangle are two downwardly extending circular housings or skirts 131 and 132, the outer corner wall of these housings being continuous with the outer corners of the main case portion 126. The walls of the body portion adjacent the handle 120 are thickened as indicated at 133 in order to provide adequate strength for the handle mounting.

The heads 122 and 123 are mounted on square stub shafts 134 and 135 which have upper threaded port-ions 136 and 137 and each of which has a lower smooth round stub portion pressed into the inner race of its respective bearing assembly. Thebearing assemblies are mounted on the heads in upstanding collars 138 and 139 rigidly secured to the top plates of the heads. The bearing assembly and construction of the head 122 are shown in section in Fig. 13 where the top plate is indicated at 140 10 and the bearing assembly is shown as comprising an inner element 141 and an outer ring or element 142 between which are arranged a plurality of ball bearings 143; the round portion of the stub shaft 134 is pressed into the element 141 as indicated at 134a. The threaded portions 136 and 137 of the stub shafts are threaded into crank arms 144 and 145, respectively, these crank arms being formed integrally with counterbalance weights 146 and 147. The crank arms 144 and are mounted on shafts 150 and 151 which are mounted in pairs of ball bearing assemblies 152 and 153 pressed into openings in the bottom wall of the case 126. Spacers 154 and 155 are arranged about the shafts 150 and 151 between the cranks and the bearings. Shafts 150 and 151 are driven by gears 156 and 157 and are rigidly secured to the gears by a locking arrangement comprising lugs 158 on each of the gears arranged to engage two sides of hexagonal heads 159 and 160 on the shafts 150 and 151 respectively. The gears 156 and 157 are driven by engagement with a center gear 161 as shown in Figs. 12 and 14. The gear 161 is provided with a shaft 162 whch is mounted in a pair of ball bearing assemblies 163 pressed into the upper end of the boss 130 in the lower wall of the case 126. The gear 161 and shaft 162 are retained in assembly with the bearings 163 by a nut 16311. The opening at the lower end of the boss 130 is closed by a suitable dust cap 164. The upper end of the shaft 162 is provided with a hexagonal head 165 which is retained in the position rigidly by lugs 158 on the gear 161. The construction of the three gears 156, 157 and 161 is identical, the three gears being of the same diameter and the shafts of the same length. This identical construction has obvious advantages both from .the standpoint of quantity production and from the standpoint of servicing the polishing machine. The gear 161 is driven directly by the motor 119 through a pinion gear 166 secured to the lower end of the motor shaft indicated at 167 which in turn carries the motor rotor indicated at 168.

The abrading machine of Figs. 11 to 15 is intended for operation at relatively high speeds. For example, the shafts 150 and 151 are rotated at a speed of the order of 3000 revolutions per minute. The translatory movement of the heads 122 and 123 is therefore rapid. The cranks 144 and 145 are made short and, for example may be of the order of five-sixteenths of an inch in effective length, that is the distance from center to center of the driving gear shaft and the shaft of the head assembly is five-sixteenths of an inch so that the small circles described by each point on each of the heads have diameters of five-eighths of an inch. The heads 122 and 123 may easily be removed from the polishing machine by unscrewing the shafts 136 and 137 from the crank arms. The threads of these shafts in the crank arms are turned so that the movement of the machine tends to tighten the shafts 136 and 137 in their positions in the arms. This facilitates the handling of the machines so that the heads do not tend to ioosen during operation. The portions of the stub shafts 134 and 135 between the crank arms and the bearing assemblies are square so that they may be held by a wrench or other device when it is desired to remove the heads from the cranks. In order to prevent rotation of the cranks when the heads are being removed, a screwdriver, naii or other object maybe inserted through openingS 170 and 171 in the skirts 131 and 132 so that rotation of the counterbalances 146 and 147 is prevented during the removal of the heads. The polishing heads 122 and 123 as illustrated are of the type and construction disclosed and claimed in my copending application, Serial No. 407,328 filed February 1, 1954. These heads as shown in the cross-section of the head 122 in Fig. 13 comprise a plate indicated at 140 to which is vulcanized or otherwise suitably bonded an enclosing envelope 172 which holds a body of cushioning material 173 in engagement'with the plate and retains it against displacement during the operation of the machine. The cushioning body extends laterally beyond the plate a distance greater than the crank radius; this further reduces pounding effects against obstructions. The head is thus of generally disk-shaped form and various types of rubbing surfaces may be secured to the head. In the embodiment'illustrated, a buffing or polishing cap has been'illustrated which comprises a neoprene rubber collar 174 and a cloth disk 175 having a pile surface 176 sewed to the lower end of the collar. The collar, when in position, holds the bufiing disk securely and prevents displacement of the disk during operation of the machine. Regardless of the type of surface secured to the polishing'heads, the operation of the machine is the same; vibration or shaking due to the reactive forces resulting from engagement of the heads against the surface being polished are reduced to a'rninimum by the balancing effect secured by the opposed positions of the headswhich rotate in the same direction and at the same speed.

The arrangement of the counterbalancing weights 146 and 147 on the outside of the casing 126 and guarded by the skirts 131 and 132 makes the counterbalancing weights readily accessible for holding the shafts against rotation when it is desired to remove the heads, the holes 170 and 171 being employed for this purpose as explained above. The-entire construction of the machine is simple-rugged and compact.

Access to the interior of the casing 126 may readily be had by first removing the motor 119 which is secured to the machine and held against the cover by a pair of bolts (not shown) which pass through openings 177 formed in thecase 126, and then removing a plurality of screws 178 which are threaded in holes 179 in the casing 126. The openings 177 are smooth openings extending entirely through the case 126 and the holes 179 are threaded and extend part way into enlargements formed in walls or partitions 180, 181 and 1.82 which partially define cylindrical chambers in which the gears 156, 157 and 161 are located. These cylindrical walls 180, 181, and 1'82'extend the entire depth of the casing 126 and provide additional support for the cover 128, as well as increasing the strength of the casing 126. When the cover plate 128 and motor are removed, the pinion or gear 166 is withdrawn from engagement with the gear 161. After the cranks 144 and 145 and the nut 163a have been removed from the shafts 150, 151 and 162, the three-gears may be removed by pressing them and theirrespectiv'e shafts out of assembled relation with their respective bearing assemblies. Since all the gears are of identical construction, they may be replaced in any order and furthermoreshould a gear be broken or otherwise damaged, it may readily be replaced, it being necessary to provide a stock of replacement gears of one size only.

Obviously, the several polishing machines described herein may be employed for a wide range of-polishin'g or abraiding operations and are particularly suitable'fo'r operations wherein hand rubbing has been fou'ndtoprovide the required finish. Thus it is apparent that the particular type and nature of the surface of the heads employed on the machine is not material'and that the heads will be selected according to the requirements-of the work to be done. The term polishing head as used herein .is intended to refer to any of the varioustyp'es of heads which are suitable for-use in machines of this character and includes brushing heads, abraidin'g heads and scrubbing heads as Well as'those heads commonly employed in bufiing and polishing operations.

Polishing machines constructed .in accordancewith this invention have been found to provide consistent and highly satisfactory results generally superior to fan'd more uniform than those to be secured by hand polishing-operations. The machine is easy to handle and may readily be moved over the surfaces to be treated and involves no objectionable shaking or vibration. Duringtheoperationof the-above-described machines which -have freely rotatable heads, the heads upon contact withth'e'workto be treated are held against rotation about their centroidal axes by the drag against the work and by the inertia of the head and their movement is therefore essentially translatory, although slight drifting about the crank pins occurs and is useful in securing superior operating characteristics. Portable abrading machines embodying this invention when employed with sandpaper head surfaces are particularly useful in accomplishing smooth and exact sanding of a flat surface adjacent walls or other projections, the sanding being accomplished without gouging of the surface and without sanding or gouging of the projecting wall or other surface.

Obviously, the action of the cranks and the freely rotatable mounting of the heads may be secured by any mounting which provides a single supporting pivot for the head and the required eccentricity and free rotation, the structural form of the crank arm being merely a matter of choice; and, as used in the claims, the term crank includes all devices which provide the required crank arm or eccentricity of mounting for the heads.

The operation of the abrading machine of thi invention is simple and requires a minimum of skill to secure highly satisfactory results both in polishing and in rougher abrading operations. Thus the machine may be used easily by a novice and is admirably suited for use in home workshops and the like as well as in operations having very exacting requirements such as those of aircraft servicing.

While specific types of machines employing this invention have been illustrated and described, various modifications and applications will be apparent to those skilled in the art and it is not desired that the invention be limited to the structural details illustrated and described-and it is intended by the appended claims to cover all modifications which fall within the spirit and scope of the invention.

I claim:

1. In a machine of the class described a plurality of heads, means for separately and eccentrically mounting said heads, said heads being freely rotatable with respect to said mounting means, means for imparting a substantially translatory non-linear motion to each of the heads, and means interconnecting the heads to limit their rotation about their respective centroidal axes while undergoing their translatory motion.

2. In a machine of the class described a plurality of heads, means for separately and eccentrically mounting said heads, said heads being freely rotatable with respect to said mounting means, means for imparting a substantially translatory non-linear motion to each of the heads, means disposed between each of the mounting means and .its head permitting said'head to tilt and follow uneven portions of a surface being worked upon, and means interconnecting the heads to limit their rotation about their respective centroidal axes While following their translatory motion.

3. A portable rubbing machine of the hand manipulated type comprising, a body portion, a pair of spaced parallel shafts rotatably mounted in said body portion, motor means for driving said shafts in the same direction, two work heads, means for mounting said heads eccentrically on respective ones of said shafts and afiording free rotation for said heads about their centroidal axes, said mounting means positioning said heads'for simultaneous engagement with a work surface, the eccentricity of each of said heads with respect to its shaft being less than one-half the width of thehead, and a handle secured to said body portion and positioned a substantial distance laterally of the plane of said shafts whereby a stable three point support is provided for" the machine when held by the operator.

4. A portable rubbing-machine of the hand manipulated type comprising, a body portion, apair of'spaced parallel shafts rotatably'mounted in said body portion, motor-means for driving said shafts in 'the same'direction and at the same speed, two work heads, means for mounting said heads eccentrically on respective ones of said shafts and affording relative rotation of said heads with respect to said eccentric mounting means, said mounting means positioning said heads for simultaneous engagement with a Work surface, the eccentricity of each of said heads with respect to its shaft being less than one-half the width of the head, said heads being eccentric in opposite directions with respect to one another whereby reactive forces against said machine upon simultaneous engagement of said heads with the working surface are substantially balanced out, and a handle secured to said body portion and positioned a substantial distance laterally of the plane of said shafts and substantially equidistant therefrom whereby a stable three point support is provided for the machine when held by the operator and the load is divided equally between said heads.

5. A portable rubbing machine of the hand manipulated type, comprising a body portion having a motor and driving mechanism, a pair of spaced parallel shafts rotatably mounted in said body portion and connected to be driven by said mechanism in the same direction and at the same speed, a pair of work heads, eccentric drive means for mounting said heads on respective ones of said shafts and affording free rotation of said heads about their centroidal axes, counterweights on said driving mechanisms for balancing the centrifugal forces of said heads, the eccentricity of said heads being small as compared with the width of said heads, the eccentric positions of said heads being opposite and their eccentricity equal whereby the reactive forces upon simultaneous engagement of said heads and a working surface are substantially balanced out, and a handle secured to said body portion and positioned a substantial distance laterally of the plane of said shafts whereby a stable three point support is provided for the machine when held by the operator.

6. A portable rubbing machine as set forth in claim including means affording tilting movement of said heads with respect to their shafts.

7. A portable rubbing machine of the hand manipulated type comprising a body portion, a pair of spaced parallel shafts rotatably mounted in said body portion, motor means for driving said shafts at substantially the same speed, two Work heads, means for mounting said heads eccentrically on respective ones of said shafts and affording free rotation of said heads about their centroidal axes, counterweights connected to said shafts for balancing the centrifugal forces of said heads, said mounting means positioning said heads for simultaneous engagement with a work surface, the eccentricity of each of said heads with respect to its shaft being less than onehalf the Width of the head, and a handle secured to said body portion and positioned a substantial distance laterally of the plane of said shafts whereby a stable threepoint support is provided for the machine when held by the operator.

8. A portable rubbing machine of the hand manipulated type as set forth in claim 7 wherein each of said heads comprises a rigid hub portion and a body of cushioning material secured thereto and extending radially beyond the rigid portion a distance at least as great as the eccentricity of said heads.

9. A portable rubbing machine as set forth in claim 7 including means affording tilting movement of said heads with respect to their shafts.

10. A portable rubbing machine of the hand manipulated type comprising a body portion, a plurality of spaced parallel shafts rotatably mounted in said body portion and positioned symmetrically with respect to an axis in a plane normal to said shafts, motor means for driving said shafts in the same direction and at substantially the same speed, a plurality of work heads, means for mounting said heads eccentrically on respective ones of said shafts and affording free rotation of said heads about their centroidal axes, the eccentricity of each of said heads with respect to its shaft being less than one-half the width of the head, said mounting means positioning said heads for simultaneous engagement with a work surface, said heads being mounted on their shafts successively out of phase by substantially the same angle whereby the reactive forces against said body upon simultaneous engagement of the heads with the work are substantially balanced out, and a manipulating handle secured to said body.

11. A portable rubbing machine as set forth in claim 10 wherein each of said heads includes a rigid hub portion and a cushioning body secured thereto and extending radially beyond the rigid portion a distance at least as great as the eccentricity of the head.

12. A portable rubbing machine of the hand manipulated type comprising a body portion, three equally spaced parallel shafts rotatably mounted in said body portion, motor means for driving said shafts in the same direction and at substantially the same speed, three work heads, means for mounting said heads eccentrically on respective ones of said shafts and affording free rotation for said heads about their centroidal axes, the eccentricity of each of said heads with respect to its shaft being less than one-half the width of the head, said mounting means positioning said heads for simultaneous engagement with a work surface, said heads being mounted on their shafts successively out of phase by an angle of substantially degrees whereby the reactive forces against said body upon simultaneous engagement of the heads with the work are substantially balanced out, and a handle secured to said body and extending a substantial distance laterally of said shafts.

13. A portable rubbing machine of the hand manipulated type comprising a body portion, a pair of spaced parallel shafts rotatably mounted in said body portion, motor means for driving said shafts in opposite directions at substantially the same speed, two work heads, means for mounting said heads eccentrically on respective ones of said shafts and affording free rotation for said heads about their centroidal axes, counterweights connected to said shafts for balancing the centrifugal forces of said heads, said mounting means positioning said heads for simultaneous engagement with a work surface, the eccentricity of each of said heads with respect to its shaft being less than one-half the width of the head, the centroidal axes of said heads being positioned to move symmetrically with respect to a line normal to the plane of said shafts and midway between them, and a handle secured to said body portion and positioned a substantial distance laterally of the plane of said shafts whereby a stable three point support is provided for the machine when held by the operator.

14. In a machine of the class described two heads mounted on spaced axes for free rotation with respect thereto, means for imparting a non-linear translatory motion to each of the heads to cause them to travel in the same direction and to move bodily toward and away from one another, and means interconnecting the two heads to limit their rotation about their respective centroidal axes while undergoing their translatory motion.

15. In a machine of the class described two heads mounted on spaced axes for free rotation with respect thereto, means for imparting a non-linear translatory motion to each of the heads to cause them to travel in the same direction and to move bodily toward and away from one another, and means interconnecting the two heads to limit their rotation about their respective centroidal axes while undergoing their translatory motion, said means including relatively movable telescoped members.

16. In a machine of the class described two heads mounted on spaced axes for free rotation with respect thereto, means for imparting a non-linear translatory motion to each of the heads to cause them to travel in 2,759,305 15 16 opposite directions and to move bodily toward and away References Cited in the file of this patent from one another, and means interconnecting the two heads to limit their rotation about their respective cen- UNITED STATES PATENTS troidal aXes while undergoing their translatory motion. 157,261 Wood Nov. 24, 1874 17. In a machine of the class described two heads 5 233,067 Buzzell Oct. 12, 1880 mounted on spaced axes for free rotation with respect 862,747 Miller Aug. 6, 1907 thereto, means for imparting a translatory motion to each 1,142,570 La Hodny June 8, 1915 of the heads to cause them to travel in opposite direc- 1,430,214 Carrie Sept. 26, 1922 tions, and means interconnecting the two heads to pre- 1,868,507 Roos July 26, 1932 vent their rotation while undergoing their translatory 10 1,873,011 Modglin Aug. 23, 1932 motion, said means including relatively mova l tele- 2,171,060 De Spirt Aug. 29, 1939 scoped members. 2,365,232 Wert Dec. 19, 1944 18. In a machine of the class described a plurality of 2,367,663 Champayne Jan. 23, 1945 heads, means for separately and eccentrically mounting 2,395,537 Crosby Feb. 26, 1946 said heads, said heads being freely rotatable with respect 15 545 942 Crosby et 1 M 20, 1951 to said mounting means, means for impartinga tran l 2, 14,3 9 obins Oct. 21, 1952 tory non-liner motion to each of the heads and for moving said heads bodily toward and away from one another, FOREIGN PATENTS and means interconnecting the heads to limit their rota- 342 690 Italy Aug 14 1936 tion about-their respective centroidal axes while follow- 20 4 41 4 ing their translatory motion, said last named means also permitting the heads to tilt in any direction while travelling in their translatory paths and including relatively movable telescoped members. 

